Gas and liquid chromatography are processes used in analytical and preparative chemistry. Typically, a stationary porous material is held in a vessel, such as a column, while a sample compound in a carrier fluid passes through the porous material. In some cases, the stationary material is an inert powder coated with a stationary liquid agent.
Various distinct chemical compounds contained in a carrier fluid can have varying affinities for a stationary phase. Consequently, as the mobile fluid moves through a chromatographic column, various chemical compounds are delayed by varying times due to their interaction with the stationary phase. These various compounds emerge from the column at different times and are detected individually by, for example, a refractometer, an ultra-violet light detector or some other analytical apparatus in which the fluid flows upon leaving the chromatographic column.
Much of the effort in the development of chromatography apparatus and techniques seeks to idealize the distribution and flow of a mobile phase through a porous stationary phase. Some work has been directed to the design of end fittings to connect components through which a fluid flows. Such connectors generally should be leak resistant and mechanically stable, and should optimize the initial distribution of a mobile liquid at the top of a column.
Problems associated with the design and use of connecting components are particularly difficult in high-pressure chromatography. Pressures in the range of, for example, 1,000 to 5,000 psi or higher can be used in liquid chromatography. Consequently, dependable sealing techniques should be used. Problems arise in, for example, assuring an adequate seal without excessive wear of deformed metal parts. For example, some fittings have ferrules which are tightened about a tube. After use, the shape of a tube or column can be distorted by the force exerted on the ferrule during tightening of end fittings.
One approach to making a high-pressure connection utilizes a connector that includes a compression screw and ferrule. In such a device, the liquid seal between a tube and another component is achieved by compressing the ferrule against both an orifice of the component and the tube to both seal and stabilize the tube. Maintenance of a desired position of a tube can be desirable to eliminate “dead volume” between the end of the tube and the component, and to avoid pressing the tube axially against the orifice with an undesirable force.